630 STRUCTURE OF THE BULB, PONS, & MID-BRAIN. [CH. XLIV. 



come together at the jugular foramen, but separate again into two 

 branches, the inner of which, arising from the medulla, joins the 

 vagus, to which it supplies its motor and some of its cardio- 

 inhibitory fibres, which are of the small medullated variety, whilst 

 the outer, consisting of large, medullated fibres, supplies the 

 trapezius and steruo-mastoid muscles. The external branch, 

 which is the larger of the two, is composed almost exclusively of 

 motor fibres. The internal branch of the accessory nerve supplies 

 chiefly viscero-motor filaments to the vagus. The muscles of the 



SUP. PED. OF CEREBELLUM 

 MIDDLE 



Fig. 465. Diagrammatic representation of dorsal aspect of medulla, pons, and mid-brain. 



larynx, all of which are supplied by branches of the vagus, derive 

 their motor nerves from the accessory ; and (which is a very 

 significant fact) Vrolik states that in the chimpanzee the internal 

 branch of the accessory does not join the vagus at all, but goes 

 direct to the larynx. The crico- thyroid, however, receives fibres 

 which leave the bulb by glosso-pharyngeal rootlets ; whether 

 it receives special accessory fibres as well is uncertain. 



12. The hypoglossal nerve arises from a large celled and long 

 nucleus in the bulb, close to the middle line, inside the combined 



